Wireless LAN systems are operated based on any of an ad hoc mode which is one-to-one connection and an infrastructure mode which is one-to-many connection centering on an access point. In particular, in the infrastructure mode, a plurality of terminals share one transmission channel (hereinafter merely referred to as channel), so that a data collision is likely to occur. In consideration of this, with respect to the wireless LAN system, priority control is made in such a manner that, first, the operating conditions of the channel are checked prior to the transmission of data (packets), and when the channel is not used, after being putting on standby for a predetermined time (AIFS), the data is transmitted after a lapse of a predetermined random time (referred to as a backoff time).
In the priority control, the data is transmitted after a lapse of “random time” for each terminal, so that simultaneous transmission is unlikely to occur, thereby substantially reducing the frequency of the data collision. The “random time” is referred to as contention window (CW). The CW is changed in accordance with the number of retransmissions, and its minimum is represented as CWmin, and its maximum is represented as CWmax. Information such as the AIFS and CW (CWmin, CWmax) above is referred to as a bandwidth control parameter, in general, as a QoS (Quality of Service) parameter.
On the other hand, with respect to the wireless LAN system, the communication of a best-effort scheme is carried out, and when communication is concentrated, real-time system communication, in particular, such as voice and images, is likely to be affected, whereby the interruption of the voice or the disruption of the images occurs. Therefore, according to IEEE 802.11e, the traffic in wireless sections is classified into priorities having four classes (AC: Access Category; hereinafter, merely referred to as a category), and appropriate QoS parameters are set for each category. The categories are exemplified by “voice” (AC_VO), “image” (AC_VI), “best-effort” (AC_BE), and “background” (AC_BK), wherein the order of priority is represented by AC_VO>AC_VI>AC_BE>AC_BK.
Accordingly, a right to use the channel is preferentially provided for the real-time system data such as the voice and images (AC_VO or AC_VI), rather than for other data (AC_BE or AC_BK), so that the interruption of the voice or the disruption of the images is prevented from occurring.
With respect to conventional technologies regarding the wireless LAN communication device which carries out the priority control for each category, the following technologies have been known.
<First Conventional Technology>
Patent Document 1 discloses the technology in which the impartiality of an upward/downward ratio is realized by dynamically changing the QoS parameters (AIFS, CWmin, and CWmax).
<Second Conventional Technology>
Patent Document 2 discloses the technology in which different CWmin and CWmax are set for the QoS parameters regarding a plurality of SSIDs.
<Third Conventional Technology>
Patent Document 3 discloses the technology in which the validity of data transmission request of the category (AC_VO) having the highest priority is determined, and invalid data transmission request is refused.
<Fourth Conventional Technology>
Patent Document 4 discloses the technology in which the priority control is made in accordance with each quality characteristic (suppression of traffic delay or maintenance of throughput characteristics) with respect to video conferences and video streams, out of applications which are classified into AC_VI.
<Fifth Conventional Technology>
Patent Document 5, for example, discloses the technology in which medical instrument like a DASH device (device used to collect patient monitoring data such as ECG, heart rate, and blood pressure) can obtain a QoS requirement which is different from that of CITRIX device (device used to perform remote observation for patient data) based on a patient monitoring requirement, so that the setting for at least one of MAC parameters of a specific node (terminal) of the medical instrument and the like is adapted in such a manner as to satisfy a threshold value (the throughput level of the minimum signal required at the specific node, the time delay of the maximum signal, and the like) regarding the specific node (terminal).